The power plugs and sockets in general use are of various specifications, as shown in FIG. 21. These plugs and sockets have to be used in same-to-same correspondence, while plugs of a certain specification can not be used on sockets of other specifications. This causes tremendous inconvenience. Therefore, there have already been so called "versatile sockets" for sale which combine sockets of several configurations together.
Accordingly, several technical solutions have been proposed for combining two or more plugs and among them, a "versatile plug" has been disclosed by the Chinese Patent 87202252. The object of the plug of this Chinese Patent is to provide a plug pluggable into power sockets of various structures, and the technical solution of which is to exploit the technical feature that the distance between the centers of the two pin holes of the existing power sockets or the two power pins of the existing plugs remains unchanged to design the pins to be rotatable, so that the above mentioned design objective can be realized.
The Chinese Patent 87207492 discloses a multi-usage adjustable power plug", which provides a power plug with adjustable pin distance and changeable flat pins and round pins. The solution is that a plug body is adopted with two round pins mounted on the front end of said body, and two flat pins are sleeved on the round pins with the distance of the pins being adjustable by changing the opening of the body.
The Chinese Patent 89217984.8 discloses a "universal power plug", the object of which is to design a power plug which will fit into either round or square sockets, and into either two or three slots. The technical features of this patent are that all the prongs are designed in double bevelling cylindrical shape, wherein the grounding prong can be folded back and hidden.
However, the specification of the plug and socket is determined by the number and shape of their pins and slots as well as the distance and angle between the pins or the slots. Many different plugs and sockets can be formed by the permutations and combinations of the four factors, i.e., number, shape, distance and angle. The insufficiency of the above mentioned patented techniques lie in that they have not taken into consideration all the variations of said four factors, and in fact, the distances between the hot line slot and the neutral line slot for different sockets are not all the same, the adjustment range of the distance between the pins adjusted by the size of the opening of the pin body is rather restricted, and it can not satisfy the requirement of close parallel contact of the pin prong with the slot terminals, which is subject to unsatisfactory contact or even damages.